✓ Two crowns ✓ Same mass, different density ✓ Vertical slider ✓ Slider works ✓ Slider controls crowns — Slider direction correct ✓ Full slider range ✓ Fall animation ✓ Water displacement ✓ Rising water level ✓ Splash effects ✓ Physics correct ✓ Live mass value ✓ Live volume value ✓ Live density value ✓ Live displaced water ✓ Gilded displaces more ✓ Heureka animation ✓ No external deps ✓ Light bg / dark text ✓ Self-contained HTML
Slider direction is inverted (value=0 at top puts crowns in air, which is visually correct per spec, BUT the writing-mode+direction CSS flips the visual thumb so that dragging down increases value, meaning the label says "lower crowns into water" with arrow pointing down — needs careful audit; physics values are solid gold 19.3/silver-mix 8.65 with correct same-mass, larger-volume logic, but volume and density readouts are static rather than live-updating.
Slider direction is inverted (value=0 at top puts crowns in air, which is visually correct per spec, BUT the writing-mode+direction CSS flips the visual thumb so that dragging down increases value, meaning the label says "lower crowns into water" with arrow pointing down — needs careful audit; physics values are solid gold 19.3/silver-mix 8.65 with correct same-mass, larger-volume logic, but volume and density readouts are static rather than live-updating.